Milk drying optimization pays off

Rockwell's dairy dryer solution at Murray Goulburn is based on a model-predictive control algorithm, and allows up-to-the-minute control of dryer temperatures based on real-time moisture readings. Source: Rockwell Automation.

The engineers at Murray Goulburn Cooperative are acutely aware of the complexities involved in the milk drying process. Murray Goulburn is Australia’s largest milk processor and one of the country’s largest exporters of processed foods. Two years ago, it adopted a new system to automatically monitor and precisely control the most critical part in the manufacture of powdered milk—the final drying stage.

Murray Goulburn’s operation near the village of Koroit (Victoria) uses four dryers with capacities from 1.2 to 7 tons per hour to process skim milk and whole milk into a variety of dairy-based powders. The dryers have steel chambers, standing up to six stories high and 66 feet in diameter.

One of the critical variables that affects the quality of the powder is its moisture content. Depending on its end use, the powder should contain between approximately 3 to 6 percent moisture. The key to achieving the right moisture level is to control the temperatures of the air entering the tower, static fluid bed and vibrating fluid beds.

In the past, plant operators manually changed temperature setpoints to control throughput and moisture content. These decisions were based on the operator’s experience and using feedback from moisture samples taken once an hour. Tests on samples taken every hour showed the moisture would often vary by as much as 0.3 percent. To create a more consistent product, the temperature setpoints would need to be adjusted automatically, based on a predictive model of the dryer.

“We knew we needed an automated system to reduce the moisture variability of the powder,” says Geoff Rome, automation and utilities engineer at Murray Goulburn. “Our goal was to find a solution that would help us maintain consistent quality while increasing final product throughput.”

To meet its goals, Murray Goulburn selected Rockwell Automation’s dairy dryer solution, based on Rockwell Software’s Model Predictive Control (MPC) and Optimization technology. The Predictive Quality–Soft Sensors system continually collects data every 15 seconds from each dryer and uses predictive models to calculate optimum temperature setpoints for controlling and maintaining the desired moisture level during production.

The software manages variations in the milk solids concentrate as well as incoming air, humidity and other factors that affect drying efficiency. By reducing moisture variability, the average moisture target can be increased without compromising product quality. This allows higher yields to be produced from the same milk solids, increasing dryer capacity and reducing energy usage per ton of finished product.

“The MPC solution from Rockwell Automation performs as well as your best operator, 24 hours a day, seven days a week,” Rome says. “The result is the highest-quality product—consistently.”

With the implementation of the model predictive control solution, the moisture variability levels in each dryer were reduced on average by 52 percent, far exceeding Murray Goulburn’s expectations of 35 percent. As a result, the company has produced on average an extra ton of powdered milk product per day across its four dryers.